1. Field
The present application generally relates to optical metrology of a structure formed on a semiconductor wafer, and, more particularly, to evaluating a profile model to characterize the structure to be examined using optical metrology.
2. Description of the Related Art
Optical metrology involves directing an incident beam at a structure, measuring the resulting diffracted beam, and analyzing the diffracted beam to determine a feature of the structure. In semiconductor manufacturing, optical metrology is typically used for quality assurance. For example, after fabricating a structure on a semiconductor wafer, an optical metrology tool is used to determine the profile of the structure. By determining the profile of the structure, the quality of the fabrication process utilized to form the structure can be evaluated.
In one conventional optical metrology system, a diffraction signal collected from illuminating a structure (a measured diffraction signal) is compared to simulated diffraction signals, which are associated with hypothetical profiles of the structure. When a match is found between the measured diffraction signal and one of the simulated diffraction signals, the hypothetical profile associated with the matching simulated diffraction signal is presumed to represent the actual profile of the structure.
The hypothetical profiles, which are used to generate the simulated diffraction signals, are generated based on a profile model that characterizes the structure to be examined. Thus, in order to accurately determine the profile of the structure using optical metrology, a profile model that accurately characterizes the structure should be used.